The present invention relates to optical fibre communications systems and in particular, discloses a method of suppressing noise in an optical fibre communications system.
In optical fibre telecommunications systems, a laser is modulated with a transmission signal with the output of the laser being fed over an optical fibre of quite some distance. At the end of the optic fibre a receiver is placed for receiving and decoding the transmitted signal.
Due to Rayleigh Backscattering (RB) from the fibre system (See K. D. Laviolette, xe2x80x9cThe impact of Rayleigh Backscatter induced noise on QPSK transmission with Fabry-Perot lasers"" IEEE Photon. Technol. Lett., Vol 10, no. 11, pp 1644-1646, November 1998.xe2x80x9d), it is often the case that the fibre waveguide provides for optical feedback to the laser system which can in turn, in common with discreet reflections, introduce an instability in the laser and thereby degrade system performance. The presence of Rayleigh Backscattering normally requires the utilization of an optical isolator so as to isolate the feedback from the lazing system. The utilizing of optical isolators can dramatically increase the cost of an optical fibre telecommunications system.
It would be desirable to substantially reduce the effects of Rayleigh Backscattering without the need to utilize an optical isolator.
In accordance with a first aspect of the present invention, there is provided in an optical fibre lasing system including a feedback laser system interconnected with an optical waveguide, such as an optical fibre, a method of reducing the feedback effects from Rayleigh backscattering comprising the step of: subjecting portions of the optical waveguide to low frequency mechanical vibration so as to reduce feedback from Rayleigh backscattering of the optical waveguide.
The Low frequency mechanical vibration can comprise a continuous oscillation in the range of 300 Hz to 2500 Hz or 300 Hz to 40 KHz.
The mechanical vibration of the optical waveguide preferably occurs substantially adjacent to the interconnection with the laser system.
In accordance with a further aspect of the present invention, there is provided an optical communications system comprising a laser source; an optical waveguide interconnected to the laser source to carry an optical signal from the source to an optical receiver; an optical receiver interconnected to the optical waveguide for decoding the signal; and a mechanical modulator adapted to substantially continuously mechanically perturb a portion of the optical waveguide so as to reduce Rayleigh backscattering from the optical waveguide.
The mechanical modulator can be in contact with the optical waveguide or the mechanical modulator can emit an audio signal in the presence of the optical waveguide. The mechanical modulator preferably interacts with an initial portion of the optical waveguide substantially adjacent the interconnection with the feedback laser.
The optical waveguide can comprise an optical fibre and further preferably can include a portion having an offset core with the mechanical modulator perturbing the portion.